The enthalpy of the material is computed as the sum of the sensible enthalpy, , and the latent heat, :
|=||specific heat at constant pressure|
The liquid fraction, , can be defined as
Equation 24.2-3 is referred to as the lever rule .
The latent heat content can now be written in terms of the latent heat of the material, :
The latent heat content can vary between zero (for a solid) and (for a liquid).
In the case of multicomponent solidification with species segregation; i.e., solidification or melting with species transport, the solidus and liquidus temperatures are computed instead of specified (Equations 24.2-5 and 24.2-6).
For solidification/melting problems, the energy equation is written as
|where||=||enthalpy (see Equation 24.2-1)|
The solution for temperature is essentially an iteration between the energy equation (Equation 24.2-7) and the liquid fraction equation (Equation 24.2-3). Directly using Equation 24.2-3 to update the liquid fraction usually results in poor convergence of the energy equation. In FLUENT, the method suggested by Voller and Swaminathan [ 386] is used to update the liquid fraction. For pure metals, where and are equal, a method based on specific heat, given by Voller and Prakash [ 385], is used instead.